1. Field of the Invention
The present invention relates to an image communicating apparatus, a control method therefor, and a storage medium storing a program therefor.
2. Description of the Related Art
In addition to facsimile (to be referred to as FAX hereinafter) transmission using a PSTN (Public Switched Telephone Network), there is provided FAX transmission using a network (IP network). FAX transmission using the IP network is defined by T.38 of ITU-T recommendation. In this FAX transmission, a digital signal transmitted according to the conventional T.30 protocol is transmitted intact, thereby implementing higher-speed transmission, as compared with T.30. SIP (Session Initiation Protocol) is used as a call control protocol for the FAX transmission to implement Point-to-Point communication on the IP network. There is also known a technique of implementing FAX transmission by G3 FAX transmission between the IP network and the PSTN via a VoIP GW (Voice over IP GateWay) having a conversion function between the T.38 procedure and the T.30 procedure.
In the general configuration of a communication system via the IP network and the PSTN, a communication apparatus on the transmission side is connected to the IP network, and performs FAX transmission according to the T.38 procedure. At this time, the communication apparatus issues a SIP calling signal to the VoIP GW via the IP network. Upon receiving the signal, the VoIP GW specifies a connection partner, calls and connects a communication apparatus as a transmission partner via the PSTN, and performs FAX transmission along a path “transmission source communication apparatus—IP network—VoIP GW—PSTN—transmission destination communication apparatus”. In this case, FAX transmission is performed between the transmission source communication apparatus and the VoIP GW according to a T.38 digital transmission procedure. The VoIP GW converts the T.38 procedure into the analog T.30 procedure, and T.30 as a G3 FAX procedure is executed between the VoIP GW, the PSTN, and the transmission destination communication apparatus.
FIG. 8 is a sequence chart for explaining a procedure along the path “transmission source communication apparatus—IP network—VoIP GW—PSTN—transmission destination communication apparatus”. As a call connection procedure before such transmission is performed, some VoIP GW makers perform connection by a call for voice transmission and then perform reconnection by a call for image transmission. FIG. 8 shows this procedure.
A transmission source communication apparatus 800 transmits a SIP INVITE signal as a call connection signal to a VoIP GW 801 via the IP network. The INVITE signal includes a parameter representing the type of data to be transmitted, which is called a medium. In this example, m=audio is set, that is, call connection for voice transmission is requested. Upon receiving the signal, the VoIP GW 801 dials a PSTN 802 to send a call signal to a transmission destination communication apparatus 803. In response to this, the communication apparatus 803 sends a SIP 200 OK signal as a response signal to the communication apparatus 800 via the IP network. Upon receiving the signal, the communication apparatus 800 connects a call to the communication apparatus 803. This procedure temporarily ends the connection for voice transmission.
The VoIP GW 801 transmits a SIP INVITE signal with medium information indicating data (m=image) to the communication apparatus 800 to switch to a call for data communication. Upon receiving the signal, the communication apparatus 800 returns a SIP 200 OK signal, and connects a call for data communication. This completes call connection for FAX data communication. After that, communication between the communication apparatus 800 and the VoIP GW 801 is performed according to the T.38 procedure, and FAX communication between the VoIP GW 801 and the communication apparatus 803 is performed according to the T.30 procedure. Issuing an INVITE signal to change the characteristics of a session during the session in this way is called reINVITE.
Assume that the communication apparatus 800 has an automatic redial function. The automatic redial function is a function of automatically redialing to perform transmission at an interval set by the user the number of times set by the user when transmission abnormally ends or when a transmission destination communication apparatus is in use (busy). The communication apparatus 800 also includes a function called a count-limited redial function of limiting the redial count to one regardless of a user setting value depending on the type of a transmission destination device. When the transmission destination device is determined as a device other than a communication terminal, retransmission by redial is meaningless. The function prevents such an unnecessary redial, and is mainly standardized in North America and Korea.
FIG. 9 is a sequence chart for explaining a processing sequence when a transmission destination device is busy in communication via the IP network, VoIP GW, and PSTN.
In this example, if communication abnormally ends during an IP FAX transmission phase, a FAX transmission procedure has already been performed with the transmission destination device, and the transmission destination device can thus be determined as a communication terminal. Therefore, the communication apparatus redials according to the normal automatic redial procedure instead of the count-limited redial function. In this case, since the process has transited to the FAX transmission procedure, it is possible to determine the transmission destination device as a communication terminal but a call may be disconnected at a call control stage. A representative example is a case in which the transmission destination device is in use (busy). If the transmission destination device is busy, the process has not transited to the FAX transmission procedure, and thus it is impossible to reliably determine whether the transmission destination device is a communication terminal. Since, however, the transmission destination device may be a communication terminal, the communication apparatus redials according to the normal automatic redial procedure instead of the count-limited redial function by regarding the transmission destination device as a communication terminal. Furthermore, if a call connection is established with the transmission destination device but the FAX procedure does not advance, it is possible to determine the transmission destination device is not a communication terminal, the count-limited redial function is performed at the time of redial.
Referring to FIG. 9, the transmission source communication apparatus 800 first sends a SIP INVITE signal with a medium: audio (m=audio). The VoIP GW 801 receives the signal, and dials the PSTN 802. If, however, the transmission destination device is in use, the PSTN 802 sends a busy signal (400-Hz intermittent sound). Upon receiving the signal, the VoIP GW 801 sends a SIP 486 busy signal to the communication apparatus 800. Upon receiving the signal, the communication apparatus 800 determines that the transmission destination device is in use and may be a communication terminal, and thus redials according to the normal automatic redial procedure instead of the count-limited redial function.
As a literature associated with redial using a SIP signal, for example, Japanese Patent Laid-Open No. 2004-112182 is disclosed. In Japanese Patent Laid-Open No. 2004-112182, a calling side is notified of a redial interval using a parameter Retry-After of a SIP 486 busy signal indicating that a transmission destination device is busy. Upon receiving the notification, the calling side controls an interval until a call is originated next time in accordance with the redial interval. However, Japanese Patent Laid-Open No. 2004-112182 discloses neither an error redial function nor a method for detecting that a partner device is busy other than a 486 busy signal.
As described above, the VoIP GW which connects a voice call with m=audio and then reconnects a data communication call (m=image) notifies by a method other than a SIP 486 busy signal that the transmission destination device is busy. For example, after a voice call is connected (a SIP 200 OK signal is sent), it is notified by, for example, a busy tone using a voice packet that the transmission destination device is busy. In this case, it is impossible to determine whether the transmission destination device is busy, and start the FAX procedure. As a result, the count-limited redial function unwantedly operates instead of the normal automatic redial function. This limits the redial count to one, thereby missing an opportunity to establish communication by retransmission.